Metals are commercially extracted from minerals (ores) which are compounds of metals mixed with soil, limestone, sand, and rocks. Metallurgy is defined as a process used for the extraction of metals in their pure form at low cost and minimum effort. It deals with the process of purification of metals and the formation of alloys. The various processes involved in the extraction of metals from their ores, and refining are known as Metallurgy.
For the purpose of extracting metals from ore, all the metals are grouped into three categories:
Extraction of Highly reactive metals.
Extraction of Moderately reactive metals.
Extraction of less reactive metals.
EXTRACTION OF HIGHLY REACTIVE METALS
The highly reactive metals placed high up in the reactivity series are extracted by the electrolysis of their molten chlorides or oxides.
During the process of electrolysis, the negatively charges electrode i.e. the cathode, acts as a powerful reducing agent by supplying electrons to reduce the metal ions metal.
During the electrolysis or electrolytic reduction of molten salts, the metals are always produced at the cathode (negative electrode).
The process of extraction of highly reactive metals involves the following steps:
During the electrolysis process, where electric current is passed through a molten metal chloride, then pure metal is produced at the cathode (negative electrode) and chloride gas is formed at the anode (positive electrode).
When a molten metal oxide is electrolysed by passing electric current, then pure metal is produced at the cathode (negative electrode) whereas oxygen gas is formed at the anode (positive electrode).
EXTRACTION OF SODIUM METAL
Following reactions take place at the two electrodes during the electrolysis of molten sodium chloride:
The positive sodium ions (Na+) are attracted to the cathode (negative electrode). The sodium ions take electrons from the cathode and get reduced to form sodium atoms (or sodium metal):
Thus, sodium metal is produced at the cathode (negative electrode).
The negative chloride ions (Cl–) are attracted to the anode (positive electrode). The chloride ions give electrons to the anode and get oxidised to form chlorine gas: